Aluminum welding by combining a diode laser with a pulsed Nd:YAG laser

Laser welding of aluminum alloys (AA 5754 and AA 6016) by superimposing a pulsed Nd:YAG laser with a continuous wave (cw) diode laser has been investigated in order to improve the weldability and the process efficiency. The low absorption of laser radiation at a wavelength of 1064 nm and the high thermal conductivity make it difficult to laser weld aluminum alloys efficiently. Therefore, a pulsed Nd:YAG laser and a low power diode laser emitting a wavelength of 980 nm were spatially superimposed. This configuration allows to enhance the absorption for the Nd:YAG welding laser due to the preheating of the diode laser. Thus, the process efficiency as well as the weld quality is enhanced. The experiments revealed that a small output power of the diode laser (<150 W) allows increasing the welding speed up to 80 % and the weld depth up to 38 %. Furthermore, the superposition leads to a significant improve of the weld seam quality, in particular to avoid hot cracking.